Identification of critical factors that convert malignant cells into invasive or metastatic cells will lead to novel therapies to treat metastatic disease. We found that N-cadherin which is upregulated in aggressive breast cancers, initiates profound changes in tumor cells, inducing motility and invasion of basement membranes, activating intracellular signaling, and stimulating matrix degrading enzymes. These are hallmarks of epithelial to mesenchymal transition (EMT) associated with metastatic progression. To study EMT and metastasis in breast cancer, we are utilizing an in vivo mouse model in which the polyoma middle T oncogene (PyMT) and N-cadherin, are co-expressed in the mammary epithelium (the PyMT-N-cad mouse). Bitransgenic mice exhibit increases in pulmonary metastasis and extravasation relative to control mice. N-cadherin caused enhanced FGFR1, MAPK activation, and matrix metalloprotease-9 expression as well as upregulation of the EMT inducing transcription factor, Slug. We hypothesize that EMT, extravasation and metastasis are primarily caused by the non-adhesive FGFR1 stimulating functionality of N-cadherin. However, it is possible that the adhesive function of N-cadherin is important for tumor-vessels interactions, thus regulating extravasation and metastatic dissemination. Resolving these mechanisms will reveal fundamental processes that stimulate metastasis. Moreover, each could be the target of different therapies. In Aim 1, we will define the EMT signaling cascade activated by N-cad/FGFR signaling, especially the involvement of the EMT inducing gene, Slug, in invasion and extravasation in vitro. In Aim 2, we will determine if the EMT signaling cascade is activated by the adhesive or signaling functionalities of N-cad in vitro and in orthotopic models. In Aim 3, we will test if the adhesive or signaling functions of N-cad are important for de novo metastasis, EMT and extravasation in transgenic mouse models. In Aim 4, we will evaluate inhibitors of N-cad adhesion or FGFR1 signaling on extravasation and metastasis in vivo. PUBLIC HEALTH RELEVANCE: We found that the EMT transcription factor, Slug, is upregulated in tumors and metastases in which N- cadherin is upregulated. We believe that N-cadherin signaling through the FGF receptor induces a cascade of events that leads to Slug induction, extravasation and metastasis. We will rule out the role of N-cadherin adhesion in this process. We believe these studies will broaden our understanding of mechanisms that regulate breast cancer metastasis and will provide insights into therapeutic application.